1. Field of the Invention
This invention relates generally to interconnecting local area networks and more specifically to interconnecting ethernet networks using a token bus network backbone.
2. Description of the Prior Art
Local area computer networks (LAN) are installed in stand alone networks known as segments. Each segment connects all of the computers of a specific group. The segments can each comprise a different company department, such as an accounting or engineering department. Messages are transmitted in packets along the network. Each packet contains information identifying the source computer and the computer to which the message is intended. Each computer on the network typically has a filter which screens out messages which are not intended for it. One type of network commonly used as a local area network is the ethernet network.
Devices called bridges are used to connect different segments together. If there are several segments, then a bridge is used to connect each segment to the next segment in the series. When the bridge receives a message packet, it looks at the destination code and determines if the message is intended for a node in that same segment. If it is, then the bridge can ignore it. If it is intended for a node not in that segment, then the bridge passes the message over to the next adjacent segment. The message is passed along from segment-to-bridge-to-segment until it reaches the proper destination segment.
A problem with this way of connecting segments is that the entire system becomes increasingly inefficient with each additional segment. This is because each message must hop from segment-to-segment until it reaches its destination. Thus, the traffic load is increased in each segment between the source segment and the destination segment.
Another problem with this type of system is that ethernet networks cannot be used over long distances. A token bus network can be used to cross long distances. However, transmitting between an ethernet and a token bus network has proved difficult due to the differences in the medium access control protocols of the networks.